1. Field of the Invention
The present invention relates to a method of measuring a distance between two devices, and more particularly, to a method of improving precision of measuring a distance between two devices using a low clock rate signal.
2. Description of the Related Art
In general, radio waves are used to measure a distance between devices A and B. FIG. 1 is a view illustrating a process of measuring a distance between devices A and B according to the prior art. The process of measuring the distance between the devices A and B according to the prior art will now be described with reference to FIG. 1.
The device A transmits radio waves to the device B in operation S100 so as to measure a distance between device A and device B. In this case, the device A counts a clock of a clock signal having a uniform clock rate upon transmitting the radio waves. In general, the radio waves are transmitted at a light speed. The device B receives the radio waves and processes the radio waves in operation S102. In other words, the device B performs predetermined processing to re-transmit the radio waves to the device A.
The device B transmits the radio waves having undergone the predetermined processing to the device A in operation S104. The device A stops counting the clock and calculates a count value in operation S106. The device A measures the distance from the device B using the count value. Here, the device A calculates the distance in consideration of a time required for transmission and reception of the radio waves after subtracting a time required for the predetermined processing at the device B therefrom.
For example, if the clock frequency of the clock signal counted by the device A is 100 MHz, the radio wave moves 3 m for a clock of the clock signal. Thus, if the count value of the device A is “100,” the distance between the devices A and B is 150 m. Also, if the clock frequency of the clock signal counted by the device A is 10 MHz, the radio wave moves 30 m for a clock of the clock signal. Thus, if the count value of the clock at the device A is “100,” the distance between the devices A and B is 1500 m. As described above, a movement distance of the radio wave for a clock varies with a clock frequency of a counted clock signal. An error in a measured distance depends on the clock frequency of the counted clock signal. As the clock frequency of the counted clock signal is high, the error in the measured distance is small. As the clock frequency of the counted clock signal is low, the error in the measured distance is large. In more detail, if the clock frequency of the counted signal is 100 MHz, the measured distance has an error of 3 m. However, if the clock frequency of the counted signal is 10 MHz, the measured distance has an error of 30 m.
Accordingly, a high frequency clock signal may be used to reduce an error in the distance between the devices A and B. However, a high frequency clock signal generator generating a high frequency clock signal is more expensive and more difficult to be realized than a low frequency clock signal generator. Therefore, a method of improving precision of measuring a distance between devices using a low frequency clock signal is required.